This disclosure relates generally to marine risers connected to Blow Out Preventer (“BOP”) and used during drilling of a wellbore below the sea.
Traditional marine risers are connected to a subsea BOP. They include a central tubular as well as a series of “auxiliary” lines that provide various functionality for BOPs and risers. They are designed assuming that the BOP forms an effective pressure barrier so the risers are not required to hold pressures as high as the shut in wellbore pressure or “worst case discharge” pressure. However, new drilling systems may now utilize a surface BOP, and thus the marine risers are required to hold pressures as high as the shut in wellbore pressure. Also, in cases of failure of the subsea BOP, marine risers that hold pressures as high as the shut in wellbore pressure may provide an additional pressure barrier and may improve the safety of drilling operations.
Components for marine risers rated to pressure levels of fifteen kilo pounds per square inch (“ksi”) or less are standard and are currently available off the shelf. These components are routinely assembled by welding. However, scaling up the size of these components to achieve pressure level ratings above fifteen ksi causes significant problems for the following reasons. The components become very heavy, and their handling during construction of the marine risers requires the upgrade of all handling systems on drill ships. Also, as the components become thicker, achieving uniform properties of the weld through the entire thickness becomes difficult, making testing of the welded part necessary. The rework of low quality welds becomes costly.
In addition, certain regulatory bodies now require that the materials making the components of marine risers are corrosion resistant, for example NACE certified.
Thus, there is a continuing need in the art for marine risers and components of marine risers that achieve pressure level ratings above fifteen ksi, and are corrosion resistant.